Many researches on methods for detecting physical and chemical information by detecting lights are underway as the importance of remote sensing is widely recognized.
As one of them, sensors for detecting flame by detecting ultra-violet rays are employed in air conditiong related products, recently.
As an example, recently in air purifiers, instead of conventional operation method controlling operation of an air purifier by detecting smoke on smoking, a new automatic operation method starting an air purifier in advance by detecting ultra-violet rays emitted from flame of a lighter or a match has been proposed.
FIG.1 is a section of a conventional ultra-violet ray sensor which has been employed in an air purifier.
As shown in FIG. 1, a conventional ultra-violet ray sensor has a shape similar to a bipolar vacuum tube having two poles 12 and 13 facing each other in a glass tube 11.
The sensor has a photoelectric pole 12 of metal corresponding to the cathode, and metal wire spaced 1 mm to the photoelectric pole corresponding to the anode forming an elliptical loop.
In a state that positive potential is applied to the anode 13, if an ultra-violet ray, transmitting the glass tube 12, reaches to the photoelectric pole 12, electrons are excited at the photoelectric pole 12 by the photoenergy.
The electrons excited at the photoelectric pole 12 are attracted to the anode 13 by the positive potential making current flow from the anode 13 to the photoelectric pole 12.
In this instant, to prevent absorption of the ultra-violet rays, the glass tube 11 is filled with inert gas, such as krypton, xenon or argon, to a pressure of several ten torts.
Operation of such a sensor for detecting ultra-violet rays, a kind of so called UVtron, is to be explained in detail, hereinafter.
Upon an ultra-violet ray is incident into the glass tube, photoelectrons are discharged from the photoelectric pole 12, and when the discharged photoelectrons are accelerated sufficiently, collisions of the accelerated photoelectrons with the gas molecules filled in the sealed glass tube 11 ionize the gas molecules.
And the collision of the ionized gas molecules with the photoelectric pole 12 discharges secondary electrons.
Because the number of necessary electrons to cause such a discharge is relatively small, it is possible to detect the ultra-violet rays from a flame in high sensitivity and high speed, and because the discharge does not stop once the discharge has been started even though the lights incident thereto had been shielded, only the detection of the existence of the incident light is possible.
Accordingly, the ultra-violet ray detection sensors are suitable for watching flame by the ultra-violet rays due to the capability of maintaining the fact of discharge once started.
This is because a flame spectrum also contains ultra-violet rays and an UVtron has a sensitivity to a wave length limited to below 280 nm, the sensivity of flame from a lighter or a match is not affected by the lights of the sun or fluorescent lamps.
However, the foregoing conventional sensor for detecting ultra-violet rays requires fabrication of individual parts in production and a high voltage transformer for applying high voltage over 400 V to the anode 13, additionally.
Therefore, the high cost of the product caused by the unit sensor as well as the driving circuit has been an obstacle in the way of employing such sensors in products such as air conditioners etc.